Method and apparatus to clean an inkjet reagent deposition device

ABSTRACT

A method is described for removing residue from a fluid deposited on the interior surface of an inkjet printhead after the printhead has contained or dispensed the fluid at least once. The method makes use of a reverse flushing technique optionally used in combination with sonication. A cleaning station for flushing an inkjet printhead with a wash fluid, rinse fluid, and/or inert gas is provided as well.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.10/233,116, filed Aug. 30, 2002, now U.S. Pat. No. 6,796,634 which is adivisional of U.S. patent application Ser. No. 09/447,624, filed Nov.22, 1999, now issued U.S. Pat. No. 6,446,642 from which priority isclaimed under 35 U.S.C. 120. The entireties of these applications areincorporated herein by reference.

TECHNICAL FIELD

This invention relates to devices used in the deposition of fluids onsubstrate surfaces and more particularly relates to a method andapparatus for cleaning an inkjet printhead used, inter alia, in thefabrication of DNA arrays.

BACKGROUND

In the fields of chemistry, biochemistry, and molecular biology, thereis a need to improve capabilities for carrying out large numbers ofreactions using small quantities of materials. As a result, there is asignificant and growing interest in employing array technologies wherethe arrays comprise an ever increasing number of distinct features on arelatively small substrate.

Many methods for making arrays of biological materials are currentlyavailable. Generally, DNA arrays are fabricated on a solid substrate bydeposition of whole DNA oligomers or complementary DNA or by in-situsynthesis of DNA oligomers. Specific methods for fabricating biologicalarrays are summarized in international patent publication WO 95/35505.This reference discusses the “dot blot” technique in which a vacuummanifold transfers a number of DNA samples from circular wells to aporous membrane. In addition, DNA sequences can also be synthesized byusing a photolithographic technique as discussed in U.S. Pat. No.5,445,934 to Fodor et al., and by using a capillary dispenser tappingtechnique as discussed in U.S. Pat. No. 5,807,522 to Brown et al. All ofthese techniques suffer from inherent limitations that reduce thecapacity for producing arrays accurately and reliably.

Arrays may be prepared by a variety of methods employed in the printingindustry that do not suffer from the aforementioned limitations. U.S.patent application Ser. Nos. 09/150,504 and 09/150,507 describe formingbiomolecular arrays by novel methods and automated devices for moving aprinthead over a print surface and for depositing the fluid compositionat desired locations on the surface. Other devices used to dispensesolutions are described in, for example, U.S. Pat. Nos. 5,658,802,5,338,688, 5,700,637, 5,474,796, 4,877,745 and 5,449,754. In essence,inkjet printing processing as applied to array fabrication involvesfeeding a fluid composition into a dispensing chamber of an inkjetprinthead and providing a stimulus repeatedly to cause the fluidcomposition to issue from a nozzle or orifice toward a substrate atdesired locations, thus forming an array of features on the substratesurface.

Central to the use of array techniques is the need to deposit uniformfeatures and to avoid cross-contamination. Both non-uniformly depositedfeatures and cross contamination can generate misleading data andthereby compromise experimental integrity. Thus, when an inkjetprinthead is used with different fluids, the head must be thoroughlycleaned after contact with each fluid. In addition, a problem withinkjet printheads in general is particulate buildup. Particulates may beintroduced into an inkjet printhead when particulate-contaminated fluidis fed into printhead through a fill port as described in U.S. Pat. No.5,777,648 to Scheffelin et al. Because the cross-sectional area of thedispensing orifice of a printhead tends to be smaller than thecross-sectional area of the fill port, it is possible to passparticulates through the fill port that cannot leave the printheadthrough the dispensing orifice. One way to minimize the introduction ofunwanted particulate matter into the printhead is to load fluid into theprinthead through the printhead's dispensing orifice. For example, U.S.patent application Ser. Nos. 09/150,504 and 09/150,507 disclose thetransfer of a fluid into a printhead through the printhead's dispensingorifice relying on capillary action.

Particulate buildup in the printhead is also problematic due to therepetitive nature of array fabrication. For example, when a biologicalarray containing thousands of features is to be fabricated, the headwill have to be loaded hundreds of times. During this process, thedispensing chamber of the head can become clogged with particulatematter. Especially during the wash out process, fluids tend to dry atthe printhead nozzle leaving residue that was originally completelysolvated or suspended as small non-agglomerated particulates in thefluid composition. When the nozzle becomes clogged with residue,droplets of fluid may fail to be fully ejected or to follow a desiredtrajectory. Thus, features become non-uniform in size and shape.Furthermore, once particulate matter becomes lodged within theprinthead, the particulate matter provides an additional surface onwhich contaminants may be adsorbed or trapped thereby increasing thechance of cross contamination.

The predominant method of cleaning an inkjet printhead or “depositiondevice” is to flush a wash fluid through the deposition device afterintroducing the wash fluid via the fill port and out the dispensingorifice of the dispensing chamber. See, e.g., U.S. Pat. No. 5,589,861 toShibata. However, the orifice of the dispensing chamber is quite small,and the orifice's smallest dimension is typically in the range of tensof microns. Therefore, the flow rate of the wash fluid is limited by thesmall size of the orifice in the printhead, and low flow rates limit theeffectiveness of cleaning. When flow rate is in the laminar flow regime,as is typical with ordinary flushing methods, the velocity of the washfluid at a surface where particulate matter adheres is theoreticallyzero. Flushing may also cause particulate matter left in the reservoirto be transported into the dispensing chamber. In addition, particulatematter may be simply too large to be passed through the dispensingorifice. Once trapped in the printhead, particulate matter may becomefurther embedded in the inner wall of the inkjet printhead as the resultof further flushing.

Another method of cleaning an inkjet head is through sonication.Sonication is a generally well known technique in inkjet printingtechnology. For example, U.S. Pat. No. 5,877,580 to Swierkowski teachessonication as a part of a method to dispense chemical fluids from acapillary device. In addition, JP08085202, JP10250060, JP10250108, andJP10250110 describe the use of sonication in conjunction with inkjetprinting technology.

It is well known in the art that sonication may effectively result indisintegration of particulate matter or dislodging of particulate matterfrom the inner surface of a printhead. U.S. Pat. No. 5,574,485 toAnderson et al., for example, provides for a method in which atransducer having a cleaning fluid thereon is placed near a nozzle. Ameniscus is formed with the cleaning fluid such that the meniscusbridges the gap between the transducer and the nozzle. Energizing thetransducer causes ultrasonic cleaning of the portion of the nozzlecontacted by the cleaning fluid. In addition, U.S. Pat. No. 5,757,396 toBruner provides a method for sonicating ink-carrying channels within aninkjet printhead while purging the channels with ink. However,sonication by itself is typically only effective on surfaces in contactwith the medium that couples the sonic energy with the surface, usuallya liquid. Furthermore, there is no guarantee that sonication willdisintegrate particulate matter too large to exit through the printheadorifice.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to overcome theabove-mentioned disadvantages of the prior art by providing a new andeffective method to clean an inkjet printhead.

It is another object of the invention to provide such a method whichallows one to dislodge and remove particulates too large to pass througha dispensing orifice of an inkjet printhead.

It is still another object of the invention to provide a such methodwherein particulates are dislodged and removed through reverse flushing.

It is a further object of the invention to provide such a method whereinparticulates are dislodged and removed though sonication.

It is yet a further object of the invention to provide such a methodwherein the printhead is dried with a gas after cleaning.

It is still a further object of the invention to provide a cleaningstation for use in carrying out the aforementioned method.

Additional objects, advantages and novel features of the invention willbe set forth in part in the description which follows, and in part willbecome apparent to those skilled in the art upon examination of thefollowing, or may be learned by practice of the invention.

In one aspect, then, the present invention relates to a method forremoving residue that has been deposited on the interior surface of aninkjet printhead where the inkjet printhead has been loaded with ordispensed a fluid at least once. The printhead comprises a dispensingchamber, a reservoir in fluid communication with the dispensing chamber,and a dispensing orifice for dispensing fluid from the dispensingchamber. The method involves, initially, transferring a wash fluidthrough the dispensing orifice into the dispensing chamber. The washfluid is suitable for removing any remaining fluid or residue therefromfrom the interior surfaces of the printhead. Then, the wash fluid isemptied from the printhead. Optional steps include substantiallypreventing the wash fluid from flowing out of the printhead through thedispensing orifice after the wash fluid has been introduced into theprinthead, rinsing with a rinse fluid capable of leaving no residueafter emptying the wash fluid from the printhead and drying with a gas,e.g., an inert gas or dry clean air, after emptying the wash or rinsefluid from the printhead.

In another aspect, the present invention relates to a cleaning stationfor cleaning an inkjet printhead having dispensed a fluid at least oncewherein the inkjet printhead comprises a reservoir, a dispensing chamberand a dispensing orifice as above. The cleaning station comprises afluid transfer channel for transferring fluids or gases from one or moreexternal sources through a transfer port into an inkjet printhead. Inuse, the transfer channel is placed against the printhead so that thetransfer port and the dispensing orifice of the printhead are in fluidcommunication, enabling transfer of fluids and gases from the cleaningstation into the dispensing chamber through the dispensing orifice. Thecleaning station also comprises a wash fluid container for holding thewash fluid, an optional rinse fluid container for holding the rinsefluid, and an optional gas container for holding the inert gas or dryclean air, each capable of fluid communication the fluid transferchannel. Furthermore, the cleaning station comprises a vacuum pump thatcan be attached to the inkjet printhead for reducing pressure within theprinthead such that fluid is drawn into the printhead through thetransfer port and dispensing orifice of the printhead. A sealingmaterial surrounding the periphery of the transfer port is provided toform a vacuum seal around the dispensing orifice. Optionally, thecleaning station further comprises means for sonicating the wash fluid.

Alternatively, the cleaning station can use a wash fluid holder (forexample, a saturated capillary medium such as a sponge, or opencontainer) which can be positioned such that wash fluid held therein isin communication with the dispensing chamber through the dispensingorifice (such as by being directly in contact with the orifice).Positioning can be accomplished, for example, by a suitable transporterwhich moves the printhead, fluid holder, or both of them. A pressurecontrol system is provided to create a pressure differential across thedispensing chamber and orifice such that wash fluid in communicationwith the orifice is transferred through the dispensing orifice into thedispensing chamber. The pressure control system may include a positivepressure source acting on the wash fluid and/or a negative pressuresource acting on the dispensing chamber (either of which source may, forexample, be a pump).

In still another aspect, the present invention relates to a cleaningstation as above except that the vacuum pump is replaced with a means toinject fluids or gases into the dispensing chamber through thedispensing orifice.

In a further aspect, the present invention relates to a cleaning stationas above wherein the cleaning station further comprises a flexiblecapillary medium that assists in presenting or conveys the wash fluid tothe printhead.

Particularly when the fluid contains a polymer (such as apolynucleotide) or a polymer precursor (such as a nucleoside compoundwhich forms a unit of polynucleotides synthesized on a substrate fromthe nucleoside compounds), the same methods can be used but with washfluid being transferred in any direction from the external sourcethrough the dispensing orifice and dispensing chamber (for example, fromthe dispensing orifice into the chamber or from the chamber through theorifice) into a waste line or waste container. As before, the wash fluidmay be sonicated while the wash fluid is in contact with a surface ofthe printhead where cleaning is desired. Optionally, such a method mayadditionally include using the printhead to dispense droplets of thepolymer or monomer to form at least a portion of an array (such as apolynucleotide array) prior to the wash fluid transfer and cleaning.

BRIEF DESCRIPTION OF THE FIGURES

The invention is described in detail below with reference to thefollowing drawings:

FIG. 1 schematically illustrates an inkjet printhead comprising areservoir, a dispensing chamber and a dispensing orifice.

FIG. 2 schematically illustrates an inkjet printhead in combination witha cleaning station of the invention.

FIG. 3 schematically illustrates the use of a flexible capillary mediumto assist in presenting or conveying a fluid to the dispensing orificeof a printhead.

DETAILED DESCRIPTION OF THE INVENTION

Before describing the invention in detail, it must be noted that, asused in this specification and the appended claims, the singular forms“a,” “an,” and “the” include plural referents unless the context clearlydictates otherwise. Thus, for example, reference to “a fluid” includesmore than one fluid, reference to “a solvent” includes a mixture ofsolvents and the like.

In describing and claiming the present invention, the followingterminology will be used in accordance with the definitions set outbelow.

The terms “clean” and “cleaning” refer to removing particulate matter orother residue from the inner surfaces of an inkjet printhead, as bychemical or mechanical means.

The term “fluid” as used herein describes matter that is substantiallyliquid. Fluids may contain minimally, partially or fully solvatedsolids. Examples of fluids include, without limitation, deionized water,salt water, alcohols, other organic solvents, and the like.

The term “fluid communication” refers to a state where fluid can flowfrom one element to another. For example, two sealed chambers with acommon wall are rendered “in fluid communication” when an aperture isprovided in the common wall to allow fluid to flow from one chamber tothe other. Two open-ended tubes connected by a valve are in fluidcommunication when the valve is open.

The terms “inject” and “injection” are used herein to refer topressuring a fluid so as to induce its directional flow. Injection doesnot necessarily imply physical penetration of an object. For example, asyringe injecting water through its tip into a chamber does notnecessarily imply that the tip of the syringe penetrates the confines ofthe chamber.

The terms “particulates” or “particulate residue” are used to refer tosolids, highly viscous liquids, residues and agglomerations thereofwithin an inkjet printhead that may impede proper dispensing function.

The term “polynucleotides” includes both naturally occurringpolynucleotides and polynucleotides in which the conventional backbonehas been replaced in whole or in part with a non-naturally occurring orsynthetic backbone, and those in which one or more of the conventionalbases have been replaced with a synthetic base capable of participatingin Watson-Crick type hydrogen bonding interactions. Polynucleotidesthen, include compounds produced synthetically (for example, PNA asdescribed in U.S. Pat. No. 5,948,902 and references cited therein) whichcan hybridize in a sequence specific manner analogous to that of townaturally occurring polynucleotides. Polynucleotides include single ormultiple stranded configurations, regardless of the source, where one ormore of the strands may or may not be completely aligned with another.While probes and targets as may be described herein will typically besingle stranded, this is not essential. A “nucleotide” refers to asub-unit of a polynucleotide and has a phosphate group, a 5 carbon sugarand a nitrogen containing base, as well as analogs of such sub-units. Anoligomer (such as an oligonucleotide) generally refers to a polymer ofabout 10 to 100 monomer units (such as nucleotides) in length, while a“polymer” (such as a polynucleotide) includes a multimer having anynumber of monomer units. Polynucleotides described herein, such as cDNA,typically have between 100 to 10000 monomer units. Examples of oligomersand polymers include polydeoxy-ribo-nu-cleotides, polyribonu-cleotides,polypeptides, polysaccharides, and other chemical entities that containrepeating units of like chemical structure.

The terms “sonicate” and “sonication” refer to vibrating or introducingvibrations in an object at ultrasonic frequencies. Ultrasonicfrequencies are generally at least about 20 kHz and more particularlyare in the range of approximately 40 kHz to 200 kHz. Sonication of anobject may be achieved by applying direct mechanical action to an objector through coupling the object to ultrasonic waves with a couplingmedium, typically a fluid.

The term “surfactant” is used herein to describe a compound capable ofreducing the surface energy in the interface between a solid surface anda fluid, typically a liquid, to provide a higher degree of wetting ofthe surface by the fluid. Surfactants used herein include anionic,cationic, nonionic and amphoteric surfactants.

The present invention in general terms is directed to a method forcleaning an inkjet deposition device, i.e., an inkjet printhead, using a“reverse flushing” technique. Unlike ordinary “forward flushing” methodsin which the wash fluid is flushed out of a printhead through itsdispensing orifice, the present invention employs a “reverse flushing”process where the wash fluid initially enters the dispensing orifice ofthe printhead. The present invention further differs from ordinaryforward flushing processes in that in a preferred embodiment of thepresent invention, the wash fluid is substantially prevented fromleaving the printhead through the dispensing orifice, and theeffectiveness of the reverse flushing process for cleaning the inkjetprinthead is enhanced by sonication.

The invention is now described in detail herein with reference to thefigures. FIG. 1 is a simplified schematic illustration of an inkjetprinthead 10, comprising a reservoir 12 for holding a supply of fluid.The reservoir 12 may comprise a single chamber, as illustrated in FIG.1, or it may comprise multiple chambers for holding a plurality offluids. The reservoir 12 is in fluid communication with a dispensingchamber 14 disposed within the printhead. As shown, the dispensingchamber 14 also is a part of the reservoir 12. Alternatively, thedispensing chamber 14 may be physically separated from the reservoir 12,but in such a case a means for ensuring fluid communication between thetwo would be required. In addition, the printhead 10 comprises adispensing orifice 16 in fluid communication with the dispensing chamber14. Typically, a fill port 18 is provided in fluid communication withthe reservoir 12, and, in use, sample fluid is typically loaded into thereservoir 12 through the fill port 18. Depending on the design of theprinthead 10 and the properties of the fluid to be dispensed, however,fluid can also be loaded into the reservoir 12 through the dispensingorifice 16. When the printhead 10 is in operation, the fluid from thereservoir 12 flows into the dispensing chamber 14 where energy isapplied to the fluid. The energy can be applied in a variety of ways,such as through piezoelectric or thermal means. As a result, fluid isejected from the dispensing chamber 14 through the dispensing orifice16. The design of typical inkjet printheads orients the dispensingorifice 14 opposite a substrate 20 such that the fluid to be dispensedis ejected onto the substrate 20. Once the printhead 10 has been engagedin operation, i.e., the fluid has been either loaded or fired throughthe dispensing orifice 16 at least once, the fluid will have wetted theinner surfaces of the reservoir 12, the dispensing chamber 14, and thedispensing orifice 16. The printhead 10 must therefore be cleaned inorder to be used with different fluid without cross contamination.

As shown in FIG. 1, the typical fill port 18 has a much larger diameterthan the smallest dimension of the typical dispensing orifice 16.Typical dispensing orifice sizes for inkjet printheads are in the orderof tens of microns while fill ports can be as large as or larger thanthousands of microns. Thus, particulates larger than the dispensingorifice 16 can be introduced into the printhead 10 through the fill port18. In turn, the dispensing orifice 16 can act as a filter for theexiting fluid by retaining particulates, agglomerates, impurities orother solids in the inkjet printhead 10. Once a particulate is lodgedwithin the dispensing orifice 16, the particulate is subject to forcesresulting from the flow of fluid from further operation of the printhead10. In addition, if the fluid is a solution in which solids aresolvated, the particulate may nucleate and grow in size as liquid isevaporated from the dispensing orifice 16. Evaporation may occur inalmost any type of printheads, but may be particularly problematic inthermal inkjet printheads under certain conditions. Thus, a trappedparticulate may become tightly jammed and embedded within the dispensingorifice 16 or the dispensing chamber 14.

While the present invention may be used to clean inkjet printheadshaving only one dispensing orifice, the invention can be also employedto clean other types of printheads. For example, printheads may havemore than one orifice or dispensing chamber where the orifices may bedisposed on a common surface. The applicability of the invention to suchalternative printhead configurations will be apparent to one of ordinaryskill in the art given the following description of the invention aspertaining to an inkjet printhead having a single dispensing orifice.

To clean the printhead 10 and thereby remove embedded particulates, acleaning station 100 may be used as shown in FIG. 2. A cleaning station100 of the present invention comprises a transfer channel 105 fortransferring fluids from one or more external sources though transferport 110 into inkjet printhead 10. In use, the transfer channel 105 isplaced against printhead 10 so that the transfer port 110 and thedispensing orifice 16 of the printhead 10 are in communication, enablingtransfer of fluid from the cleaning station 100 into the dispensingchamber 14 through the dispensing orifice 16. The transfer port 110 hasa sealing material 111 around the periphery thereof thereon capable offorming a vacuum or other type of seal or gasket around the dispensingorifice 16. The sealing material 111 can comprise a variety of materialsincluding, but not limited to, natural and synthetic rubbers such aspoly(styrene-butadiene rubber), poly(butadiene),poly(ethylene-propylene), silicone elastomers, polyurethanes and thelike. In addition, a wash fluid container 120 is provided for holding awash fluid 121 and capable of fluid communication with the transfer port110.

FIG. 2 shows a version of a cleaning station of the present invention.In FIG. 2, a cleaning station 100 is shown with three containers orsources of fluids, a wash fluid container 120, a rinse fluid container130, and a gas container 140. Each of these three containers isconnected to the transfer port 110 through the fluid transfer channel105 by a separate valve. These valves can be any number of typesincluding, without limitation, ball, gate and solenoid valves. Thedefault position for all three valves is closed. During operation of thecleaning station, the valves are controlled such that no two valves areopen at the same time. Electronic means (as shown) are a preferablemeans to provide selectable control of these valves. Thus, at most onlyone container is in fluid communication with the fluid transfer channel105 at a time. Furthermore, the cleaning station 100 can be used incombination with vacuum means 150 to generate a vacuum or reduce thepressure within the printhead 10, such as a house vacuum or vacuum pump.Methods and means for generating a vacuum or reducing the pressurewithin the printhead 10 will be readily apparent to those of ordinaryskill in the art. Numerous vacuum technologies and associated literatureare widely and commercially available. In the present invention, avacuum is generally applied to the reservoir 12, i.e., a house vacuum orvacuum pump is connected to the fill port 18 of the inkjet printhead 10to reduce the pressure within the inkjet printhead 10. A wastecollection vessel 151 may be provided to collect the matter that isdrawn out of the printhead by the vacuum means 150.

In operation, the transfer port 110 is placed against the inkjetprinthead 10 such that the fluid transfer channel 105 extends fromdispensing orifice 16. As shown in FIG. 2, the sealing material 111surrounds the dispensing orifice 16 to form a barrier capable forholding a vacuum. In addition, the wash fluid container 120 is filledwith a wash fluid 121 and deployed in a manner such that the wash fluid121 can flow through the transfer port 110. As shown in FIG. 2, fluidcommunication is achieved between the wash fluid container 120 and thetransfer port 110 when a wash fluid valve 122 between the wash fluidcontainer 120 and the transfer port 110 is opened. When a vacuum isgenerated within the printhead 10, the wash fluid 121 is drawn from thewash fluid container 120 through the wash fluid valve 122, the transferport 110 and the dispensing orifice 16 into the dispensing chamber 14 ofthe printhead 10. The flow of the wash fluid 121 tends to dislodge andsuspend particulate matter adhering to the inner surface of theprinthead 10 as well as those trapped in the dispensing orifice 16. Oncewash fluid 121 is introduced into the printhead 10, it is desirable toprevent the wash fluid 121 from later flowing out of the inkjetprinthead 10 through the dispensing orifice 16, since there may besuspended residue particulates left in the wash fluid 121, and theparticulates may again be lodged in the dispensing orifice 16. This canbe done by ensuring that the vacuum remains engaged and that no netforce is applied to the wash fluid 121 in the dispensing direction.Alternatively, a wash fluid 121 can be chosen such that capillary forcesare employed prevent the wash fluid 121 from exiting therethough. Thewash fluid 121 should be emptied from the printhead 10 without allowinga substantial portion of the wash fluid 121 to flow through thedispensing orifice 16 again. Preferably, no more than a minority portionof the wash fluid is removed through the dispensing orifice. Morepreferably, no more than about 20 volume percent of the wash fluid isremoved through the dispensing orifice. Still more preferably, no morethan about 10 volume percent of the wash fluid is removed through thedispensing orifice.

In certain instances, a sample fluid to be deposited by a printhead maybe loaded into the printhead through the printhead's dispensing orifice.See, e.g., U.S. patent application Ser. Nos. 09/150,504 and 09/150,507.In such a case, vacuum means may be employed to draw the sample fluidinto the printhead. Such vacuum means may also be used to draw wash orrinse fluid for cleaning the interior surfaces of the printhead.However, because loading and cleaning often require different flowrates, a proportional valve disposed between the vacuum means and theprinthead may be used to regulate the flow rate of the fluid drawn intothe printhead. Usually, the sample fluid is loaded into the printhead ata slower rate than the rate at which a wash or rinse is drawn into theprinthead for cleaning purposes.

When particulate matter strongly adheres to inner surfaces 13 of theprinthead 10 or is tightly lodged within the dispensing orifice 16,sonication may be desirable in addition to reverse flushing as describedabove. Sonication is a well known art, and many commercial ultrasonicdevices are available and can be adapted to the present invention.Sonication can be applied to the printhead 10 through direct mechanicalaction or preferably by using the wash fluid 121 as a coupling medium.While the wash fluid 121 is in contact with the desired surfaces forcleaning, the wash fluid 121 is sonicated by an ultrasonic transducer115. The location of the ultrasonic transducer 115 is not critical andmay be placed wherever effective to cause cavitation at the surfaces tobe cleaned and to dislodge the particulate residue adhered thereto.Sonication should be applied for a time period sufficient to ensure thatno particulate matter remains lodged within the printhead. Typically,sonication should be applied for about one second or less to dislodgeparticulate matter, longer if desired. Once particulate matter, isdislodged, it is suspended by the wash fluid 121 and flushed out of theinkjet head 10 with the wash fluid. The printhead 10 can be sonicatedanytime while a wash fluid is in contact with the surfaces to besonicated, before, during or after reverse flushing. Sonication mayadditionally enhance the removal of nonsolid matter such as residualfluid by improving overall cleaning dynamics.

Optionally, a reverse flow sponge touch method can be additionallyemployed to present or convey wash or rinse fluid to the dispensingorifice. FIG. 3 shows a capillary medium 112 disposed within a transferport 110 that is in fluid communication with a fluid transfer channel105. An ultrasonic transducer 115 is located within the fluid transferchannel 105. In operation, the capillary medium 112 presents the washfluid to the printhead allowing it to draw the fluid into the printhead.Typical capillary media is sufficiently soft or flexible such thatcontact with the dispensing orifice will not result in damage. Inaddition, capillary medium must be wettable and have a sufficientlylarge surface area on which wicking of fluids may occur. When the washor rinse fluid is an aqueous fluid, the medium should have sufficienthydrophillic properties to act as a sponge to hold the wash or rinsefluid. Such materials are generally known in the art. In addition, thematerial should have sufficient mechanical integrity such that little orpreferably no additional particulate matter is introduced into thecleaning process, i.e., the medium should not shed. The flexiblecapillary medium may be in a variety of forms that includes, but notlimited to, porous pads, bristles, webbing, cloth, and fabric. Themedium 112 may also help couple the sonic energy generated by theultrasonic transducer 115 to the printhead 10. When a flexible capillarymedium is employed, a seal is not necessarily required for the cleaningstation.

It should be emphasized that it is not necessarily possible to eliminatethe problem of particulate buildup by attempting to eliminateparticulate matter from the fluid to be deposited. First, very littlefluid is used to deposit features in the formation of an array;typically, the starting volume in the reservoir is in the range ofmicroliters and each feature requires only tens or hundreds ofpicoliters of fluid. Filtration may not be practical with such a smallvolume. Second, when the printhead is used to deposit biochemicalagents, the fluid may contain biomolecules such as oligonucleotides,polynucleotides, oligopeptides, polypeptides, proteins or otherbioorganic or organic materials, typically in a buffered aqueous fluidcontaining anionic and cationic species such as sodium, potassium,lithium, calcium, magnesium, zinc, nitrates, sulfates, phosphates,citrates, bromides, chlorides, fluorides and the like. When water isevaporated from such a solution, salts and other crystals canprecipitate out of the fluid, thereby depositing particulate matterwithin the printhead. Third, the printhead, fluid lines, air, valves andall other parts of the system can be sources of contamination. In otherwords, even if particulate matter can be eliminated from the fluidbefore the fluid is loaded into the printhead, particulate matter canstill be formed within the printhead.

With the above understanding of the problem of particulate buildup, itis evident that the preferred wash fluid comprises a liquid that willdissolve all solid materials from the fluid remaining in the printhead10. Residue is solvated when the residue has a similar solubilityparameter as the solvent. For example, a protein typically will have asimilar solubility parameter as another protein, and thus one proteinwill typically solvate another protein. Similarly, a hydrocarbon willtend to solvate another hydrocarbon. Because ionic species such as saltprecipitates are highly polar in nature, a polar solvent must beselected to solvate ionic fluid residues. Solvents that have sufficientpolarity to solvate ionic species typically employed in fluids used infabrication of nucleic acid arrays include water, alcohols, ketones,dimethylsulfoxide, dimethylformamide and the like. Where the fluidcontains a mixture of polar and non-polar components, alcohol can be asuitable wash fluid. Generally, any alcohol is suitable that has ahydroxyl group appended to a branched or unbranched saturatedhydrocarbon that is a liquid at room temperature. More particularly,lower alcohols such as methanol, ethanol, isopropanol, and the like areoptional wash fluids.

The preferred wash fluid comprises water. Because water is a componentof many biomolecule-containing fluids, using water as a wash fluidreduces the likelihood of contamination should any wash fluid remain inthe printhead after cleaning. In addition, water has excellentproperties as a solvent to dissolve salt residues that typicallyaccumulate in a printhead during typical biochemical array fabrication.Furthermore, water is available in high purity at low cost in additionto being safer and more environmentally acceptable than flammableorganic solvents. Optionally, the wash fluid may also contain asurfactant and/or an organic component to help couple water to surfacesthat are not readily wetted by water.

If a rinsing step is desired following the initial wash step, a rinsefluid container 130 for holding a rinse fluid 131 and capable of fluidcommunication with the transfer port 110 is provided, as shown in FIG.2. First, fluid communication should cease between the wash fluidcontainer 120 and the transfer port 110 before rinsing. Thus, the washfluid valve 122 should be closed. Then, the rinse fluid container 130,filled with a rinse fluid 131, is deployed in a manner such that therinse fluid container 30 fluidly communicates the transfer port 110.Thus, the rinse fluid valve 132 disposed between the rinse fluidcontainer 130 and the transfer port 110 is opened. The vacuum generatedwithin the printhead 10 draws the rinse fluid 131 from the rinse fluidcontainer 130 through the transfer port 110 and the dispensing orifice16 into the dispensing chamber 14 of the printhead 10. Then rinse fluid131 should be emptied from the printhead 10. While no particulate mattershould remain in the printhead 10 after the wash fluid 121 has beenemptied from the printhead, one may further safeguard againstreintroduction of particulate matter into the dispensing orifice 16 byensuring that the rinse fluid 131 does not exit the printhead throughthe dispensing orifice 16. This can be done using the same methods asdescribed above for preventing the wash fluid from flowing out of theprinthead through the dispensing orifice, i.e., by ensuring that thevacuum remains engaged and that no net force is applied to the rinsefluid 121 in the dispensing direction or by employing a rinse fluid 121such that capillary forces exert a force on the rinse fluid and therebypreventing the wash fluid 121 from exiting therethough.

The rinse fluid is selected such that it is able to remove any remainingwash fluid residue in the printhead. In addition, the rinse fluid shouldnot itself leave any residue within the printhead after drying. Thus,fluids containing solids, solvated or non-solvated, and liquids that arenon-volatile, are generally unsuitable for rinsing. Examples of suitablerinse fluids include, but are not limited to, pure deionized water, purealcohols, and mixtures thereof. The preferred rinse fluid may alsocontain other inert liquids that vaporize as readily as or more readilythan water without residue.

After washing or rinsing, the present invention optionally includes adrying step to remove all unwanted fluids from the printhead. There areat least three methods to dry the printhead. In one, heat is applied toevaporate any residual fluid by using ordinary radiant energy sourcessuch as heat lamps, ovens or the even printhead itself if the printheadis capable of producing thermal energy. In another, a vacuum is imposedon printhead by placing the printhead in a vacuum chamber. The preferredmethod is to expose wet surfaces within the printhead to a flow of agas, either an inert gas or clean dry air. In this method, a gascontainer for holding a gas suitable for drying the printhead isprovided. However, the gas can be from any number of sources. Referringto FIG. 2, after washing and/or rinsing, all valves should be closedexcept for the gas valve 142 disposed between the gas container 140 andthe transfer port 110. This can be accomplished through computerizedcontrols. Thus, of the three containers shown in FIG. 2, only the gascontainer fluidly communicates with the fluid transfer channel 105. Thevacuum within the printhead 10 and/or the pressure form the gascontainer draws the gas 141 from the gas container 140 through thetransfer channel 105, transfer port 110, and the dispensing orifice 16into the dispensing chamber 14 of the printhead 10. Then, gas 141, whichis either an inert gas or dry clean air, is passed over the interiorsurfaces 13 of the inkjet printhead 10 that were contacted by the washfluid 121 to dry the surfaces. Suitable inert gases include, withoutlimitation, nitrogen, argon, helium, gaseous perfluorinated alkanes andethers, gaseous chlorofluorocarbons and the like. The preferred inertgas is nitrogen. Alternatively, the gas can be introduced thorough thefill port of a printhead to dry the interior surfaces of the printhead(not shown). In such a case, one of ordinary skill would adjust the setup of the cleaning station accordingly.

In the preferred embodiment as described above, the present inventionmakes use of a house vacuum or a pump that can draw the wash fluid, andoptionally the rinse fluid and gas, through the dispensing orifice ofthe printhead. In another embodiment, the invention does not necessarilyinclude a vacuum. Rather, a means for injecting a fluid into theprinthead through the dispensing orifice of the printhead is provided.The means for injecting fluid may comprise a device as simple as aplunger to one as complex as a compressor to pressurize and inject fluidinto the dispensing orifice. Because compressors apply a positivepressure to force fluids into the printhead through the dispensingorifice, a seal to prevent fluid leakage is preferred. A vacuum seal isnot necessarily needed when a vacuum is not employed. Alternatively,means for transferring fluid may comprise both a vacuum and positive toenhance the flow rate of the fluid.

Variations on of the present invention will be apparent to those ofordinary skill in the art. For example, heat may be applied to theinkjet printhead or the wash fluid to increase cleaning efficiency. Inaddition, the preferred electronic means as discussed above that may beincluded as a part of the clean station to provide selectable control ofvalves may be adapted for other purposes.

It is to be understood that while the invention has been described inconjunction with the preferred specific embodiments thereof, that theforegoing description is intended to illustrate and not limit the scopeof the invention. Other aspects, advantages and modifications within thescope of the invention will be apparent to those skilled in the art towhich the invention pertains.

All patents, patent applications, and publications mentioned herein arehereby incorporated by reference in their entireties.

1. A cleaning station for cleaning a printhead wherein the printheadcomprises a dispensing chamber and a dispensing orifice for dispensing afluid in fluid communication with the dispensing chamber, the cleaningstation comprising: a wash fluid source for supplying a wash fluid; arinse fluid source for supplying a rinse fluid; a fluid transfer channelcomprising a transfer port which allows fluid communication between thefluid transfer channel and the dispensing chamber through the dispensingorifice; a wash fluid valve disposed between the wash fluid source andthe fluid transfer channel, wherein the wash fluid source is in fluidcommunication with the fluid transfer channel when the wash fluid valveis open; a rinse fluid source for supplying a rinse fluid suitable forrinsing the interior surfaces of the printhead; and a rinse fluid valvedisposed between the rinse fluid source and the fluid transfer channel,wherein the rinse fluid source is in fluid communication with the fluidtransfer channel when the rinse fluid valve is open.
 2. The cleaningstation of claim 1, wherein the station further comprises a means toprevent the wash fluid valve and the rinse fluid valve from being openat the same time.
 3. The cleaning station of claim 1, wherein theprinthead is an inkjet printhead.
 4. The cleaning station of claim 1,further comprising means to sonicate the wash fluid or the printhead. 5.The cleaning station of claim 1, wherein the cleaning station furthercomprises a gas source for supplying a gas suitable for drying theinterior surfaces of the printhead; and a gas valve disposed between thegas source and the fluid transfer channel, wherein the gas source is influid communication with the fluid transfer channel when the gas valveis open.
 6. The cleaning station of claim 5 further comprising means toprevent the wash fluid valve and the gas valve from being open at thesame time.
 7. The cleaning station of claim 1, wherein the cleaningstation further comprises a vacuum source attachable to the printheadfor reducing pressure within the printhead such that fluid is drawn intothe printhead through the transfer port and dispensing orifice of theprinthead.
 8. The cleaning station of claim 1, wherein the cleaningstation further comprises a sealing material surrounding the peripheryof the transfer port to form a vacuum seal around the dispensingorifice.
 9. The cleaning station of claim 1, further comprising apositioning means for positioning the wash fluid source in proximitywith the dispensing orifice for fluid communication between the washfluid source and the dispensing orifice.
 10. The cleaning station ofclaim 9, wherein the positioning means is capable of moving the washfluid source, the printhead or both the wash fluid source and theprinthead.
 11. The cleaning station of claim 1, wherein the cleaningstation further comprises a waste line or waste container for receivingfluid from the dispensing orifice or from the dispensing chamber. 12.The cleaning station of claim 1, wherein the fluid transfer channelfurther comprises an ultrasonic transducer.
 13. The cleaning station ofclaim 1, wherein the transfer port comprises a medium for holding afluid.